Prebiotic Chemstry

Jeff G. Wardeska, PhD

Jan. 24, 2008

Two Questions 1. How were the molecules necessary

for the first living organisms synthesized?

2. Could life as we know it exist elsewhere in the universe?

1. How were the necessary molecules for the first living

organisms synthesized?

What molecules are needed to make the simplest cell, e.g., virus?

1. How were the necessary for the first living organisms synthesized?

What molecules are needed to make the simplest cell, e.g., virus?– 1. Protein; 20 amino acids.

H2N CH C

CH3

OH

O

1. How were the necessary molecules for the first living

organisms synthesized?

What molecules are needed to make the simplest cell, e.g., virus?

– 1. Protein; 20 amino acids.

– 2. DNA; 4 bases (A, G, C, T), PO4-3, ribose.

N

NNH

N

NH2

Adenine

NH

NNH

N

O

NH2

Guanine

N

NH2

NH

NH

O

O

Thiamine

CytosineO

1. How were the necessary molecules for the first living

organisms synthesized?

What molecules are needed to make the simplest cell, e.g., virus?

– 1. Protein; 20 amino acids.

– 2. DNA; 4 bases (A, G, C, T), PO4-3, ribose.

N

NN

N

NH2

O

HOH

HH

HH

HO

Adenosine

1. How were the necessary molecules for the first living

organisms synthesized?

What molecules are needed to make the simplest cell, e.g., virus?

– 1. Protein; 20 amino acids.

– 2. DNA; 4 bases (A, G, C, T), PO4-3, ribose.

– 3. Proper conditions

N

NN

N

NH2

O

HOH

HH

HH

OP-O

O-

O

Today’s Atmosphere Oxidizing: N2, O2, CO2, H2O Organic Molecules are oxidized. CH4 + 2 O2 -> CO2 + 2 H2O Unique to Earth. Fe3+; Fe(OH)3, Ksp ~ 10-39.

A. I. Oparin, 1938 The Origin of Life. (Dover, 2nd edition) Original atmosphere- reducing. H2, CO, CH4, NH3, H2O, (H2S). Oxygen is the result of Life on Earth. Fe2+ primary form of iron.

Miller-Urey Experiment

1950. Reacted Mixture of

CH4, NH3, H2, H2O.

Miller-Urey Experiment 1950. Reacted Mixture of

CH4, NH3, H2, H2O.

• Produced about 20 amino acids (<2% yield, each),+ HCN.

• Reacted about 15% of C.

Miller-Urey, cont’d Can form amino acids

under a variety of conditions;– UV light energy.– Sound.– Heat.

– + H2S -> cysteine.

– HCN -> A, G– +HCCCN -> C, U

(Cyanoacetylene)

N

NNH

N

NH2

Adenine = (HCN)5

H C C C N

What’s the evidence that this chemistry might

have actually happened?

Murchison Meteorite, Australia, 1969. Geologic Record.

Murchison Meteorite Sept. 1969, Australia

Murchison Meteorite

1. Large number of amino acids, > 50 not found on earth.

2. Slight enantiomeric excess of l-enantiomers in some.

3. Diff. 15N/14N ratio from terrestial samples. Same ratio in both d & l enantiomers.

Precambrian Era, Mya

Fe(II)

Fe(III)

Fe(II)

Fe(III)

Precambrian, cont’d. 3800. Oldest rocks,

oceans form. 3500-2800. 1st

prokaryotes, photosynthesis produces O2.

2800-1600. Banded Iron Formations.

Fe(II)

Fe(III)

Stromatolites

Banded Iron Formations

Issues Origin of l-forms of amino acids. Mechanism of synthesis of

nucleosides and nucleotides. Chicken vs. egg; which came first,

DNA or proteins?– RNA world?

Are we alone?

Further reading

Stanley L. Miller and Leslie E. Orgel, “The Origins of Life on the Earth”, Prentice-Hall, 1974.

Antonio Lazcano* and Stanley L. Miller, “The Origin and Early Evolution. Review of Life: Prebiotic Chemistry”, the Pre-RNA World, and Time. Cell, Vol. 85, 793–798, June 14, 1996.

Leslie E. Orgel, “Prebiotic Chemistry and the Origin of the RNA World”, Critical Reviews in Biochemistry and Molecular Biology, 39:99–123, 2004

Thank You!